Beam switching system



June 3, 1952 E. amica ETAn:

BEAM swzm-1m@ SYSTEM 9 sheets-sheet 1 Filed May l0, 1948 Kub .EE v h mada.

.E2 RUCE /M/EA/rops L. 6R05 Mmm/5V June 3, 1952 E. BRUCE ETAL lBEM/1 SWITCHING SYSTEM 9 Sheets-Sheet 2 Filed May 10, 1948 moda.

June 3, 1952 E. BRUCE` ETAL BEAM SWITCHING SYSTEM Filed May 10. 1948 9 Sheets-Sheet 3 m, .Sk

E. BRUCE L GROSS AHORA/Ev E. BRUCE El AL BEAM SWITCHING SYSTEM June 3, i952 9 Sheets-Sheet 4 Filed May 10, 1948 sill E TTORNEV E. BRUCE ErAL BEAM swIT'lmuNG-SYSTEM June 3, 1952 9 sheds-sheet 5 Filed May 10, 1948 .5. BRUCE INVENTORS-L GROSS ATTORNEY June 3, 1952 E. BRUCE :s1- A1.,

BEAM SWITCHING SYSTEM Filed May 10, 194s 9 SQeets-Sheet 6 l m36-h Lush HIl E. BRUCE /NVEA/rops. GROSS HUM A T TORNE Y June 3, i952 E. BRuE Erm. 2,599,368

BEAM swITCHING SYSTEM Filed May 10, 1948 9 Sheets-Sheet 7 FIG. 7 NUMBER GROUP- COMMON CON TROI.

@Amm 5 OH/G/N- 7U INDIVIDUAL THUN/(S .5. BRUCE /Nl//TORS. u GROSS A T TOR/VE V EA BRUCE` El AL BEAM SWITCHINS SYSTEM June 3, 1952 9 Sheets-Sheet 8 Filed May 10, 1948 Q mm u8 .S F S 2%, b como uw ...kiq L Y SS ,EBRUCE /A/Vf/VTo/QSL. GROSS n ATTORNEY 9 sheets-sheet 9 Filed May 10, 1948 L. GROSS /A/r/EA/robs- 5 BAN/Cf Patented June 3, 1952 .rising :BEAMsWrroinNdsYs'rEii/i Edmond Bruce, Bedgank, NIJ., and Leo Gross, e Bayside; N. "Y., assignors to iBell JTelephone Laboratories;IncorporatedgNeweYorkfNY.; a corporation-of NewYork .ApplicationfMay 10, 1948,jSerial- N,o.',2,6,014

(CLy Z50-#7) Claims. 11 ;',I `his invention relates to telecommunication systems.. and.. particularly .t0 ...Switching Systems `for the establishment of interconnections between `thesubscribers stations` ofk such telecommunica- .tionystems.

"The obj ect of Athe inventionv is the attainment of great` speedin the establishment ofy connections. Heretooren particularly inj'machineswitching--or Y'dirait telephone systems very e expensive apparatus has been-@developed and used to control'the-move- -ment-of whatl now-may be-termed slow-moving Vmechanical elements -of-the system. The present invention is based on the-use of switching-means which' iscapable of completing.thezestablishment of-aconnection ina very small-fraction oa sec- `0ndas compared. to the several. seconds. heretof fore necessary.

v4'Another Aobject off .the Ainventioniis .to provide means for switching.' by` the vuse .of ,.inertialess beams :rather-.thanv through :the Yuseof; compara- .:.Jtivelymassive.mechanical elements. The move- .;.ment of thebeamsrnay be made extremely rapid since the beams themselves being inertialessmay :be-.moved practically v,instantaneously Yand 1 the i; means for. :directing the L movement thereof. as, iorinstancergby Jthe movement ofr` piezoelectric ;erystals;maybeiextremelyrapid.

v5.A11-o4ther. ol:p ect ofthe invention is to -employ I a-switching-mea-ns which a plurality of comamunication channels may be established through space-.zonH a. non-interfering 'basisn regardless of ,the fact thatany given established channel may ,-v,f-,feometrically intersect one or more-of. the other established channels.

. .Still another object .of .the invention is, to providea communicationlsystem in which the usual central ofce multiple is eliminated, that ..is,' fone ..in.w.hich. each subscribers line .or each inter- '.,Qlcetrunk linehasbuta single appearance in a switching system.

'.Theinvention in its preferred form Vdiscloses ausystem employing visible light beamsrbutA comn prehends anyv form of radiant energy which ,may 'be controlled in .theform ofrbeams. "The practical limits are from beyond 'the' low infra-.redto the extreme vultra-violet, termsA of frequency, `from A101" to 1015, ,cycles per second and are here only limited by the practical consideration of the meansfor control as; by way ofv example, the dimensions of lens and other optical systems. Statedotherwise, Vvthe f invention contemplates switchingkby-means of beamsof `transverse electromagnetic waves.

.;.Another-object ofthe linvention is to-provide a; broadl bandA switchingsystem-or-alsystemin which broad band communicationchannels may be rapidly and economically setup. yAga-infthe invention has been'disclosed,'-by way-lof example, as a telephone switching -systemibut-fma-y be ,used v.with jarir equalfacilityior other purposes such as switching-television hannels-where-the broad band-j'fe'atureeis -particularlylvaluable. v -fIt is known thatV in" mechanicalswitching -systems `the breadth of the frequencyband employedds limited: by considerations-ot cross-talk. The -use Oftbeams which are non-interfering even though they may- -intersect yirrthe geometricalsensetisa 'desirable feature lfor -this purpose.

*It isto be noted-that a-communication-channel using la radiant-.energyvbeamis-not `limitedin lthe breadth -of-a;band-that-mvay-be-transmitted as kthe conventional-pair A ofwires. It .is well.. known that lbands -of-megacycle -widthmustf -ibeachannel-le'dy-over--coaxialn conductors .and-even. wave ever,--is-notso limited and-will transmit. without any seriousattenuation Vany widebandy overwhich system and `is- -centeredabout;V the. use.-..of retro- "directive optical-means'v having. theunique ,property of-projecting the reflected .beam .back on .the lexact @line-over which .lthe'pbeamf vreached athis optical-devicesoi:that -a.- communication. channel l space over av single ugeometrically.. straightz'line. @ImaccordanceWiththis invention a. cornertre- -flector is u employed vvhi`ch...rnay. be..:.dened. asa '-deviceonsisting .of .three intersecting.. and-mufvention; however, 1.is .not limited .togthisc particu- 4lar formi Lof...optical.devicebut comprehends: the ...use of.- anyzlretrodirective. reilector. suclrfY forgin- :stancef as the-devce known asa ca'ts eye. fThis,

.-ingiaflightl` I*beam .which- ^is parabolic;v inl-contour for .two-waysignallingnmay bei-.establishede-in tually.-perpendicular.reecting` surfaces. The .in-

as-is wellknownr consists .of a; surface.' for v,receivandeisf `backed .up by. a spherical surface. placed at the exact Afocallength .of ithe,` paraboloidzwhereby .a beam :from anyzdirectioncimpinging .upon t.

'creara sphericalsurface .abackreng-thc .aexactfline over cwhich ...it .reached 5' the .parabolic .y suriace. .L-Whereasayplane reflecting surface willgonlyfreect a'=v .beam .back qn.zitself: -from the; Znhf; the

a.Wideideviationtherefrom.

theY .parabolica surface.v willabe reflected` from;- the .retro directive reflector.willso.y relect;.arbeam from ...A switching rsystem .-.isf theng; eonstrllfledby mounting 1.on.,a..surface a .largefnumben.ofzcorner ..,reectors.oneeassociatedwith A.each subscriber-s line. s" In. a' vpreferred .emb-odmentf.:ille-.inmution the pyramidal tip of..eachi.iwllerersuchob '3 ner reflector is constructed of a solid piece of glass or other transparent material having the three mutually perpendicular surfaces fashioned therefrom) may be truncated so as to pass therethrough a fraction of the beam directed thereat and a beam sensitive device mounted on or at this truncated point so as to translate beam variations into electrical signals for transmission to the associated line. Where the corner reflector is constructed of solid transparent material the front surface thereof, a plane surface substantially normal to the zenith line f such reflector, must be coated so as to be non-reflecting whereby all the light directed toward the corner reflector surfaces may be allowed to reach them and none dissipated by reflection from the other surface of the device. Alternatively a window may be otherwise formed on one or more of the surfaces near the intersection thereof, particularly where the corner reflector may be formed of mirrors. In any case, a fraction of the light beam directed to the corner reflector falls upon a beam sensitive device so that such beam as modulated at the distant end may translate the modulations thereof into electrical signals.

A beam controlling device may also be placed before said corner reflector so as to be in the path of a reflecting beam. This device being also connected to the associated line would translate electrical signals transmitted over said line into beam variations. At a distant point there will be a plurality of beam producing and beam directing devices with beam controlling and beam responsive devices connected to other lines thereat. Any one of such other lines may then signal control to its beam directing means and by thus pointing a beam to a selected one of the distant corner reflectors immediately establishes a connection between the line associated therewith and the said other line.

One simple arrangement of these means may consist of a single telecommunication exchange in which each line has an appearance in a corner reflector at one end of a room and in beam directing and translating means at the other end of the room. The appearance in the corner reflector would be termed the called line appearance while the appearance at the other end of the room in the beam directing means wouldY be known as the calling line appearance thereof.

In another arrangement, each line may have only a single appearance at which end would be four elements. First, a corner reflector; second, a beam directing means; third, a beam sensitive means; and fourth, a beam controlling means. In this arrangement, each of the units for all of the lines would be mounted on a single wall and the beams produced would be directed toward one of the other lines through the use of a mirror at the other end of the room.

In another arrangement, all the lines of an exchange would each have a single appearance in the combination of a reflector, a beam sensitive device and a beam controlling device on a single wall of the line. At the opposite wall thereof there would be a plurality of link circuit terminations each consisting of a beam directing device, a beam sensitive device and a beam controlling device. These link circuit terminations would enter a circuit arrangement whereby connections could be established between the-various lines of the exchange and the various link or vtrunk circuits.

4 would each have a pair of beam directing devices and their associated beam sensitive and beam controlling devices so that a connection could be established between two of the lines of the same exchange over two beams directed from a single link circuit termination.

A feature of the invention is a switching system in which a light beam having light directed in both directions along the same straight line is used as a two-way communication channel and having means at one end thereof to selectively direct said beam to any one of a plurality of communication channel terminations, and means at said selected termination to reflect the said beam back on itself.

Another feature of the invention consists of means at each end of a two-way light beam to absorb a fraction of the incoming beam by translating means for producing signals therefrom, and means to modulate the outgoing beam to transmit signals over said light beam to the other end thereof.l

Another feature of the invention consists in the use of a corner reflector having a truncated pyramidal tip in the rear of which is placed an outgoing beam directing means and an incoming beam sensitive Vmeans in combination with a modulating means for affecting the outgoing beam whereby all four elements necessary for a two-way light beam communication system are located at one point.

Another feature of the invention consists in the use of electroresponsive means for rotating a pair of mirrors to direct a light beam over a coordinate array of receiving points each of which employs a corner reflector to reflect the light directed thereto back on itself over the same geometrically straight line. In its preferred form piezoelectric crystals are disclosed as a practical and economical means for this purpose.

Another feature of the invention is a means for establishing a plurality of connections over straight lines in space without interference where two or more of such lines mayl intersect. Where cords are used for making connections to a great array of lines terminating in jacks the confusion and tangle of a large number of cords used simultaneously poses a mechanical problem involving cord construction, insulation, etc., to withstand the mechanical interference of the cords. In the present arrangement, there is no mechanical or other interference between the beams even where a direct or geometrical intersection of the beams takes place.

Another feature of the invention is a means for simultaneously establishing a plurality of connections to a single line whereas there will be means provided in such a beam switching system as disclosed herein to normally prevent the establishment of more than one connection to a line at a time, that is, the usual busy test functions and means will be provided. There will also be the means for establishing what are known as conference connections whereby several lines may be connectedY together simultaneously. Such connections are feasible when several light beams from different sources are simultaneously directed at the same corner reflector, for the corner reflector itself is capable of simultaneously reflecting an infinite number of light beams each back on itself from an infinite number of distant sources.

Another feature of the invention is a system legscsgses i -including a lightbeam established betweentwo corner reiiectors, one ateither end of the beam whereby `multiple reiiections on a -single straight --linemay be employed.

i-Still lanother'ieature is a system including a fplurality of lines' and a plurality of trunkswith alight" beam source' and ka beam director per ltrunk. Thistrunk may end at fa distant point -injasingle arrangement or in -some other more conventional arrangement. In accordance with rthis'vfeat-urebutfa'single light beam per trunk termination is employed.

Other features will appear hereinafter.

vThe-drawings 1' consist of nine'sheets having eleven figures as follows:

Fig. 1 is `a schematic showing one switching Yplan and illustrating-the principle of the invention;

'FigsfZ to5 arranged as shown in Fig. 10 constitute a-circuit diagram showing one embodiment of the Yarrangement'illustrated in Fig.'1 and in which Fig.` 2 shows the line' circuit, Fig. 3 shows the light beaniterminatingl arrangements, Fig. 4-shows Ythe beam positioning circuit in the common control circuit fand Fig. 5 shows the number group device in vthe .common control "device;

Figs. 2, 4,-6 and 7 'arranged as indicated in Fig. 11V show afsimilar circuit diagram as a varli'ation of the arrangement shown in Figs. 2 to `Siand in 'which Fig. 6 shows the light beam ter- Y minating arrangements and Fig.l 7 shows an elec- "tronic number group device in-the common control;

f l'Fig. 8 is -a schematic similar to that shown in Fig. 1 whereby connections are established by means of link circuits;

A Fig. 9 is another schematic similar to that of Fig. 1-showing a plan wherebyconnections are "set `up by apparatus individual to the -sub- 'scribers lines through alight beam'reflected by a plane mirror from one line appearance to another;

Fig. 1'() is'a block diagram showing how Figs. i2 -to 5- maybe arranged; and r "'Fig. 11 isfa block diagram Vshowing how Figs. 2,-4; Sand? may be arranged to provide a comi plete circuit diagram.

AThe broad outline of the telecommunication switching system using light` beams as part of the' talkingpath is set forth herein. The esjsential parts of the switching means are a light beam, modulated and directed toward a retrodirective mirror (or corner reflector). Asso- *ciate'd witheach corner reector is a photode- VVtector'and-a`modulator. This modulator im- "presses a signal on the reected beam which sig-nal is then transmitted over the beam to the distant selected point. Another photodetector 'mounted in close proximity to the light source detects the signals on the reflected beam. By directing one light beam toward a selected one of 2a plurality of retrodirective mirrors and there- 'byre'ecti'ng the lightv beam back on itself, two- 'way-communication may be established.

fSeveral switching plans'using the light beam -Ytalking paths are herein set forth. The location of the beam directors'and the light sources withrespect to the retrodirective mirrors is the distinguishing feature of each of these arrangements.

(a) lThe' arrangement shown in Fig. 1 is one vinv-which each linev appears in a retrodirective l mirror withits variousvcontrolling devicesso thata'connectionmay be set-iup by alightbeam A "directed" theretoeil'tlier.-l= from `an i-incomingetrunk appearance on an! outgoingltruiikmappearance;

lb) `The iarrangement shown in Figfisf one in which link! circuits -arel luse'd, .eachlhavinglan incoming and ani outgoing terminal'by means fiof which a light beamrnay be directed to twocli-ne appearancesthereby.interconnecting the twoand establishing comrn'unicajtion betweenfthem; `land V(c'Ihe arrangement shownin rFi'g.; f is another -variation by meansxof which leach-.line appearance has all 4of the lelements'y necessary, for establishing intercommunicationl'by. light beams so thatY -a calli-ngi line may? selectv any Lione; off; a

"number of other-.lines by-directingxafiight beam towardY the line-appearance tof. theeother y.as vreiiectednby a plane mirror-.at -the endiof :a switching-room. y

-By way of e'xamplethe lineiappearances; :that isf-the retrodirective mirrorisandfthe other-Icontrolling devices vmay `be ;mounte`d .ion-L one fwa'll of what may )beltermedafswitching.:room. "Ji'Iihe apparatus for i each .line would occupy about ...a 2-inch square -so Athatlan -arraylof 100 'x :100 to -make -a 10.000 line-exchange`fwould ll afwallfl'? feet square. -Trunkappearancesot a lessernumber, say v10 per cent ofthis,1:would bef-mounted-on a parallel wall distantv about feet. These ldimensionsare byway of exampleonly,v andfmay be varied lfor diiierentpurposes.k l

In 1 two of 10,000subscribers"stations YI and 2 are shown. -The substation I. is.' numbered 0000 and the substation?y isifnumbered 9999, it

YVbeing understood that the. other 'substations of this systemfhave othernumbers Abetweenthese two limiting values. .Each line extends from'fthe premises of a-subscr-iber to! the central-office .over atwo-wire lineknownras the tip and ring 'and each has its own line circuit-such` as thecircuits 3 and 4, respectively.

The switching-room 5 is 4V'shownasa large broken line rectangle. Within this switching room and at the left-handr wall thereof the line appearance 6 for the substationI and thexline appearance 'I for the substation 2 areshown. At the other-'end of the room, incoming-trunk appearances f 3 and 9 and outgoing.r trunk appearances I0 and II are shown. y

Thesubscriber at'substation I may through his controlof the common control lcircuit ,I2 cause a connection to be established -between the line appearance 6 and the trunk' appearance I0 for the outgoing trunk I3'extending to some distant point. yIn a similar manner a call coming in over an incoming trunk Ill may through the use of the common control circuit I2 cause a connection to be established between the-trunk appearance 9 and the `line appearance 1. The establishment of these connections consists .essentially of the direction of' a light beam from the trunk appearance either incoming or outgoing tothe retrodirective mirror in the line appearance. The details of these devices are shownand explained more fully hereinafter.

-In Fig. 8 a somewhat similar arrangementis shown. Here the subscribersv lines v I5 and I6 with their associated line circuits- I! and I8, respectively, and their associated line appearances IB'and 20; respectively, may through the use of the common control circuit ZI establish light beam connections between the various subscribers circuits. For instance, the subscriber at substation I5 through the use of the common control circuit 2I may control the link 22 so that one light beam will be established between the ktrunk appearancexZS;A and the line `appearance I5 7 of the calling line and another light beam between the trunk appearance 24 and a selected one of the lines to which a connection is desired, whereby communication may be established between substation I and the said selected substation.

In Fig. 9 another general outline plan is Vdisclosed. In this the substation 25 is connected through a line circuit 26 and thence through a hybrid coil 21 having a transmitting device 28 mounted on or associated with one of the plane surfaces of a retrodirective mirror and a receiving device 29 similarly mounted on or associated .with another of the plane surfaces of the retrodirective mirror. Associated with this line appearance there is a lamp 30 shown as a source of light with a lens 3| to create a beam which will then be reflected by two mirrors such as the mirror 32 mounted on a member 33 which is capable of a small movement so that when two of these mirrors are each moved the light beam may be directed in any desired direction. In Fig'. 9 such a light beam is indicated as being directed to a plane mirror 34 and reflected therefrom to the retrodirective mirror 35 associated with a selected subscribers line 36.

Each line, such as the lines 25 and 36, may through the use of the common control 31 cause the appropriate movements of the devices such as 33 to move the mirrors such as the mirror 32 to direct the light beam as desired.

In each of these devices or plans, communication from one station to another is effected through the modulation of the light beam at the originating end and the detection of the modulated light beam and the translation thereof at the other end. Many well known and conventional components can be used for these purposes.

LINE AND TRUNK APPEARANCES A. The line The line appearance shown in Fig. 3 consists of a lens system shown herein as the lens and the lens 4l to collect the incident beam from a distant source and concentrate a parallel beam upon the corner reflector 42 behind it. The lenses are coated to minimize optical reflections and are of short focal length so that what little light is reiiected will be widely scattered to reduce optical cross-talk. A shutter 43 operated by 'a solenoid 44 mounted behind the lenses operates when the line is in use and permits light to pass through the modulator 45 and fall upon the corner reflector which is here shown as having a photodetector 46 mounted at its truncated vertex. The photodetector 46 and the modulator 45 are connected to the lines 41 and 48 through a conventional hybrid coil 49, the photodetector acting as a receiver of incoming signals and the modulator acting as a transmitter of outgoing signals.

Since each line appearance is part of a twodimensional array, the line circuit (Fig. 2) identifies its appearance by two voltages corresponding to its coordinates in the array. Whenever the line circuit is energized, this information (or the two said voltages) is used to direct a light beam upon the line appearance in question. In the absence of a metallic path between trunk and line, supervision is maintained by the presence of the light beam. The change from dark to light current operates a light current supervisory relay (LCS) This dissipates a fraction of the signal received by the photodetector but this 8 loss may be avoided by someconventional form of trigger action circuit.

Each half of a connection in the originating and terminating omces is held up by the local substation circuit. At the termination of the connection when the line is released by the holding subscriber the shutter 43 in the line circuit is released and the shutterclosed, thereby releasing the light current supervisory relay in the trunk, thereby restoring the trunk to normal. The ringing arrangements are local to each line circuit.

'Ihe connection between the line appearance in Fig. 3 and the line circuit in Fig. 2 is as follows: The lines 41 and 4S derive talking current through the windings of a line relay 50 from a source of battery and ground and extend through the back contacts of the ringing connect relay 5I to the substation line. When the subscriber thereat makes a call the line relay 50 will be operated and will establish connections which will be more fully described hereinafter.

When the substation 52 is selected to have a connection established thereto then the ring connect relay 5| will be operated and will connect the line conductors through the windings of the ringing trip relay 53 to a source of ringing current in the conventional manner. When the called subscriber answers the ringing trip relay 53 will operate and by removing a ground connection to a holding circuit of the ring connect relay will allow this relay to release and establish the connection to the lines 41 and 48 and thence through the hybrid coil 49 to the various devices for establishing the connection over the light beam.

B. The trunk The trunk appearance shown to the right in Fig. 3 consists of a light source 55 and a lens system consisting of the lenses 56 and 51 designed to form a parallel light beam of spot size, less than an inch in diameter at the line appearance. Due to the unavoidable divergence of a light beam the light source, real or virtual, must be small (for example, not larger in diameter than .005 inch). The light beam passes through a modulator 56 and falls on the beam directors 59 and 6U. These are two mirrors mounted lat right angles to each other, one rotated in azimuth and the other in altitude. Voltages applied to their deflecting elements 6| and 62 determine their angular position and the location of the light beam on the line appearance field. The deflecting elements 5l and 62 may, by way of example, be piezoelectric crystals. The beam directors may be locked in place, once deflected, by a solenoid operated clamp. Thus a solenoid 63 controls an element 64 in such manner that when the solenoid is energized the element 64 will firmly push against the end of the beam director and hold it in the position to which it has been moved by the electrical potentials applied. A photodetector 65, placed in close proximity to the modulator 58, intercepts a portion of the reflected light beam from the selected line appearance and detects the signal thereon. A hybrid coil 66 connects the modulator and photodetector to the trunk represented by the trunk conductors 61 and 68.

An idle outgoing trunk circuit is seized in a lock-out circuit by ring a trunk tube 69 through the number group as will be explained more fully hereinafter. The location voltages of the line appearance to which a connection is to be es- 9 tablished are .applied to 4position the beam director. .A .timedelay isinserted so that the light beam is produced `after-the beam directors have come to rest andthe lightbeam does not sweep over undesired'line appearances. When thereected beam is detected the light current operates the trunk supervisory relay 10,150 complete vthe trunk circuit connection.

,An incoming trunk herein indicated by the broken line. rectangle 1| has those features of the line circuit used for initiating calls and isconventional except for the arrangements shownand described in. connection With .the outgoing trunk appearance.

THE COMNION CONTROL The common control shown in Figs. Al and 5 transmits positioning voltages from the line to the trunk circuit and checks to see that a connection has'been-established before releasing.

For the sake of simplicity it may be assumed group device which testsfor a busy or idle condition. At the completion of this test the common control has been connected toga trunkA and the vertical and horizontal voltages are applied to the beam directors of that trunk. The beam is accurately centered upon the retrodirective mirror'in the line appearance by the `beam positioning circuit. The common control then sends a clamping signal to the trunk to hold the beam directors locked in place. The common-control thenfretires.

Number group The device shown in Fig. 5 is a-conventiona1 relay arrangement whereby digits transmitted by a calling line and registered in the register -1| may be used to select a trunk characterized by a three-digit number, as by Way of examplaone leadingV to a particular exchange characterized by such three-digit number. The said number group consists essentially of a set of units, tens and hundreds relays individual to the register 1| bymeans of which corresponding three common leads may be electrically affected to select a `trunk'or some other facility characterized by such anumber.

Beam positioning circuit When'an idle circuit, whether it be a desired trunk, Vline or busy tone trunk, has been selected,

then thebeam positioning circuit of Fig. 4 comes into-operation and centers the beam produced l and controlled by the selected circuit on the retrodirective mirror of thel calling line. A series of signals applied to the V (vertical) and H (horizontal) tubes Vcauses them to pass current through the V and H resistors in the line array multiple thus controlling the deflecting voltages by v means of the IR drop. At the end of its cycle of operation, the beam positioning circuit applies a clamping voltage to the beam directors, thus completing'the duties of the common con- 10 FUNDAMENTAL OPERATION IN ESTABLlSYI-I- ING- Ay CONNECTION A calling line or trunk seizes a common control and then transmits into a register thereinan identification of the called line or trunk. The common control then causes the line or trunk Aappearance which has the ibeam establishing means to establish a beam and to then vdirectit to the otherappearance which supplies the. identifying beam directing voltages, the common control acting to modifysuch.voltages-suiicientlyto accurately position the beam.

The various line and trunk appearances-arein groups and the appearance in each group is'zin what is termed a lock-out relation tothe others so that only one at a time may be `served by the common control. The lock-out circuitgfundamentally, is disclosed in Patent 2,326;551, granted August 10, 1943 to M. E. Mohr.

Let us now trace the operations in the establishment of a connection from substation 52":to the outgoing trunlrv circuit over conductors (i1-and 68. The ysubscriber in initiating a call vestablishes a-conventional substation network through which sucient current will ow to operateI the line relay. When the commony control is free. positive battery 12 will be connected through the back contact of the mainr anode relay lv13, vthrough the winding of RS relay 14, conductor-15, resistor 16 to the main anode 11, of tube 18. 'The operationsof relay' 5|) hasfconnected positive vbattery potential'over the back contact andarmature 2 of the LOS relay 19 to the start gap-anode 8U of the tube 18. If thev potential of the start gap cathode v connected in common with-other tubes in thisn group to the inductance182 vhas not been raised too high-by reason of thel busy condition of another tube of the group then the tube will be fired at this start gap. Assumingrthat the common control is free as stated andthat, therefore, the positive potential from the battery 12 is'connected to the main anode 11, the firing ofthe tube at the start gap will now betransferred to the main gap so that current Willflow from the positive batteryover the main anode11 to the main cathode v83 through the armature `3 and back contact of the LCS relay 19, the Winding of the CC relay 84 to ground. ARelay y31| is=em ployed for effectivelyconnecting the -line circuit to the common control for an instant Aduri-rig which the number lof the lcalled line; is'transmitted tothe register, the beam established-rat a selected outgoing trunk appearance and.- the beam positioned by the common control circuit.

A connection from the tip of the line is-made over armature -2 and .back contact of the'RC relay 5|, armature 2 vand frontcontact of 'the CC relay 84, the tip Wire `|35 to the register 1|. A connection from the ring conductor ofthe line is similarly made over armature I and back contact of the RC relay 5|, armature 4 and-front contact of the CC relay 84, conductor qto-the register 1|, The register 1| is conventional and will respond to signals sent from the substation 52 to register at least a portion ofthe identification of the called line. In the present casa-the register 1| is shown as a means for operating the number group consisting of the ten units-'the ten tens and the ten hundreds relays for electrically characterizing three conductors leadingl to a trunk tube 69 for selecting the corresponding outgoing trunk. The register A1| is indicated'as having control over a connecting relay'81'so that if the UO relay 86, the TO relay-88 and thefHO .denser 94.

11 relay 90 have been operated then the three conductors leading to the trunk tube 69 will be aifected. The start electrodes of other trunk tubes may also be affected but the trunk tube 69 is the only one which will have all three so aifected and, therefore, is the only one which may be red to establish a current from its main vanode to its main cathode.

'I'he number group controlled by the register 1| will attempt to seize the called trunk and will report the busy or idle condition to relays associated with the number group at this time. The operation of the trunk tube 69 is as follows. There is a start cathode 93 connected to the units wire and a start anode with a short gap to the start cathode connected to the hundreds wire. If this res, then the secondary start anode 96 connected to the tens wire will become eiective and will take over the current ow in this gas tube so that the electron stream in the tube is transferred from the hundreds to the tens wire. If the trunk is idle then a current flow will be established between the main anode 91 and the main cathode 98. Under this condition there will then be a current ilow from the main anode 91 to the main anode 98 and a smaller current now from the main anode 91 to the start cathode 93. There will also be a small current from the secondary start anode 96 to both the main cathode 98 and the start cathode 93. However, if the trunk is busy, then the potential of the .main cathode will have been raised to the point where no current now will be established from lthe main anode to the main cathode and hence the current stream from the secondary anode 96` to the start cathode 93 will persist and be of .a volume great enough to operate the busy relay.

These operations may be followed in the circuits of Figs. 3 and 5 as follows. Upon the operation of the connecting relay 81 a circuit will be established for the momentary operation of the relay 9| during the charging period of con- During the interval that the relay 9| is operated, ground will be connected through armature I and front cont-act of relay 9| through the armature and front contact of the UO units relay, 88, thence to the start cathode 93. At the `same time positve battery will be connected vthrough the front contact and armature 2 of --relay 9|, the armature and front contact of the HO-hundreds relay 90 to the start gap anode 92.

Again, simultaneously, positive battery will be -connected through armature 3 and the .front contact of the HP relay 9|, the armature and front contact of the TO tens relay 89 to the secondary starting anode 96. If the trunk is idle 4then the ionization within the tube caused by the current ow from the secondary anode 96 to the start cathode 93 will break down the main gap of the tube so that current will flow now from positive battery, the back contact and armature of the main anode relay 13, the main anode 91, the main cathode 98 through the armature 4 and back contact of the TLS relay 10, the winding of the TC relay 99 to ground.

In case this trunk were busy such condition would be denoted by the operation of the TLS relay so that the cathode 98 instead of being Aconnected through armature 4 of the TLS relay to a ground connection as just described would `instead be connected to a positive battery connection so vthat the gap will not break down. In

this case, the action of the relays 95 and |00 should be noted. l1f the trunk is properly seized, then upon the deenergization of the relay 9| the 12 c relay will operate but the relay |00 will not be affected because the current flowing from the secondary anode 96 to the main cathode 98 Will be insufficient to operate this relay. Under this condition the conductor |02 will be grounded for a purpose which will be shortly described. If, on the other hand, the trunk is busy then the main gap does not break down and current will ow from positive battery through the winding of the relay |09, Athe armature and front contact of the TO tens relay 89, the secondary start anode 96, the start cathode 93, the front contact and armature of the UO units relay 88, the winding of the relay 95 to ground. Therefore, both relays 95 and |00 will operate and will act together to ground the line lill leading to a busy tone circuit.

Any conventional means in this connection may be used, such for instance, as a busy tone relay per line associated with the line relay 50 which could be operated through the contacts of the CC relay 84 and remain locked in until the calling subscriber recognizes the busy tone and hangs up.

A more 'economical means, however, is indicated in the drawings as consisting of another circuit similar to the outgoing trunk appearance shown in Fig. 3. In such a case where the trunk tube 69 has failed to nre because the associated circuit is busy the conductor |0| will be grounded and this will extend to a start cathode of a tube in the busy back appearance |03 so as to seize such a busy tone circuit. This circuit will then establish a beam and position it in the same manner that the beam from the circuit shown in detail is positioned and which will be described shortly. In such a busy tone trunk the tip and ring line conductors similar to the conductors 61 and 68 will in this case extend to a source of l busy tone |04. v

Let it be assumed that the outgoing trunk circuit shown in detail in Fig. 3 is idle. Therefore, when the trunk tube 69 i'lres, a circuit will be established from the main anode 91 through the main cathode 98, the armature 4 and back contact of the TLS relay 'I0 to the winding of the TC relay 99 which thereupon operates. During the short interval over which this circuit is established the presence of the common inductance |05 and the resistance |09 in the circuit of the main anode acts to depress the potential on the anodes of other tubes connected in plurality therewith and to, therefore, effectively lock out any other tube than the one now in operation.

The trunk connector relay 99 in operatingextends ground through its armature 2 and front contact through the thermistor |01 to the lamp 55 representing a source of light to establish the beam. The thermistor |01 is a device which initially has high resistance but which due to the current iiow and the consequent heating thereof will lower its resistance. Therefore, the lamp 55 will not come up to full brilliance immediately thereby avoiding the sweeping of a light beam over other line appearances during its establishment and positioning.

The trunk connector relay 99 also connects through its front contacts and armatures 3 and 4, the two beam positioning devices 62 and 6|, respectively, and thence over the conductors |08 and |09 to the beam positioning circuit in Fig. 4. nt the same time the control connector relay 84 1n Fig. 2 has connected taps for the horizontal and vertical voltages to the conductors |08 and |09. The taps for supplying these voltages are 13 showniascoming fromial precision'- batterywhich: means thatth'eyare connected Ito 'predetermined' voltage. pontsrsupplied by a batterywhich` is maintained very precisely:-

whchfv isestablishedi at-' each trunk`A appearance wllbe'positicnedaccurately atfthe centerfof 'the 'ldiwhen both' of 1`the f beam positioning devices'. are in their normally unoperated positions.L Therefore;- the -Ibeam-` maybe Amoved. horizontally: to `anyon'e of ftyf-positions t'oWard-the-right or; alternatively to any one :of the Alftypositions to ward the left. Similarly, the bea-m mayf be' moved by vthe-other beam" director to -any fone of ftypositions above oralternativelyato --any one of fty posittms` below itsfnormalpostion; Each liiieicircuit;therefore is connected' to a pairfof precision batterfylleads ofthe proper polarityfand magnitude-tofmove the beam of f a distant trunk? appearance tofv the lineappearance associated therewith.7V

Due to thegroundingof the conductor" II32a'nd-l thee-application of` the` precision battery voltages tocondctors 'H155`r and I- the bcamwill beydirected Ytovvardfth'e line appearanceas*indicatedin Fig: 3"even=though ythebeain 1may "not'yet be established'fin all ofV its brilliance.

Thebeampositioning circuitv ofFig. 4^"isf' a'4 meansffo'r accurately 'centering the beam i'which' isftransmitted' Yfrom the -trunklappearance on theV line appearancein Fig. 3; As-the'beamstrikes the line :appearance thenV the photodetect'orlv 4S" bei comes 'active t'and the current ow vtheretlircugli and -thencethrough theresistance `I I i3; 'theWnd-g ingofth'efLCS lrelay V19; through the v`front contactv andarmaturef'of the line relay 5c t'o` ground jin` creases." The-lead connected to the armature 6 andffr'onticontact ofgthe CC relay 38d 'andthence overy conductorJ I I Ij therefore,V carries a.' potential lneasure'dby" the drop which is the productiefA tlefcurrentflowing'in-'the photodetector 'L55 and the-#resistancel` of thefLCSv relay ''and'V there`` sister-*I I0? Therefore; as the beambecomes es'- tablisliedftlie voltage ori-conductor `I I IV rises.

The devicelrepresented by-the rectangle II2isv awoltagearnpliier which may4 be in 'the form` of, ai: conventional vacuum4 tube voltme-terf This when it isrena'bled by the-ccnnection-ofground tos. conductor- IIl2v communicates g the` voltage changes inztheconductor: I Ii to the dii'erentiator II'3i`1 Thissisuaz'device consistingessentiallx'f offa smallecondenser'andfa -resistance which Vupon the application of avoltage-V thereto Wil1" produce -a positive signal. in the'form-oia positive impulseof short". duration... Asv-"th'e beam-fis? moved to thephotodetectori 46: itis: knowinglyv` movedslightlyv than is actually necessary so'V that as the beam-is' being-centered the voltage on conductor! I I'rises andthenfbegins; tofdecrease; As soon-as the voltage reachesits: peak value andfbegins" to decreasethe diierentiator III generates anegative signal. These positive and negative signa-ls are transmitted by the ldiierentiatorto the' Vsignalgreversal i counter I I 0.- to sequentially: Venergize the Wave form generators H5;` I I6; l I1 and'l I8;l The generatorsl I5 Yand IIB controlthetubef! I9 and '.the-fgeneratorsg I I7 andA I lcontrollthe Atube I2L.Y These tubes are known asrvariable-gm tubes and-.each responds;l totlie' potential .applied "to its grid tocauseza largeror smaller amount'offcur'f rent .1 to owfinitsiianode'ecathodecircuiti The `14 and; therefore, vas the :current-increases-'thefdrop inthe-resistor I 2 I increasesiso that: thepo'tential of the=condi`ictori H185 therefore somewhat de@- creases. H'ence, when the rising voltage foficon ductor: II-I is communicated tothe-Waveform Y olierentiator I I3sends a negativeI impulse :whichoperatesthe signal reversal counter I l'totranse fer from the waveA form 'generator' IIE'4 tof4 the Waveform generator.` IIIi and this now reduces the' potential on the gridof tl'letube` I`I9by `a small cleniteamount whereby thepotentalfoff conductor I throughlV the smallerh amount-'- of current'flowingV through 'resistorl 2 I Ais `allovvedfto rise a` smaller and'- denite amount to 'exactlycenter the beam on the' line appearance retro#- directve mirror-142. The"-changefromffaf falling potential on conductor III to a:- risingfpotentiafl now causes the di'erentiator II.?,"tooperateto send another pulse Which now enables the-Wave ormfzgeneratorj I I'I so that'n"this-fsame'manner the-beam as'controlled by y.theelement i6 I isf-Scen-` tered'inithe lior'izontal direction.' A

The dierehtiator 'isra deviceeknown- 'as/an RG pea-ker andfza' description -of suona-devicemay be foundin the Pri1ciples ofRadar;` a'v-piiblicatin:

"V of the-Technology Press; Massachusetts Ins'titiite'j of"Technolo'gy,l published by thai McGaW=Hi11 Book Company, Incorporated," 1946;" pagesiZllfT' et" secr; Reference mayA also be. made'in" thev volumeV to pages 3-12` et" seqi'under: VSwe'e'p VoltageY Circuits and 'particularly' topage's"`3`20.l

under. Sweepj'ntegrating 'Circuits 'Where means to insure'a constant potential; at the vendwoffa sweepmay b'e incorporated'in the diffrentiatr. II3.

The signalf'reversal counterisfa conventionalchainof countingftubes which-respondsftothev positiver and .negative pulses generatedzandtransfmittedby the Vdiiierentiator I vrI 3.* Ameferenceitoi adevice o this nature maybesfound in a volume entitled =Tirne Bases by G, S: Puckle-,,pi1blished: a-tl -NewJ-Ycrk John Wiley? and it Sons-,eIncorporated. Schmitts trigger-circuit;.pages'iletsect2;` isfa device" which: will operate: inathe.V 'desired k manner:

Thr-is; asf, the: beam is.: establishediitiscatoi matica-lly--centered byfrneans-f of-tl`1"e'#bean-1*'pcisifv tioning f circuitY (Fig: .43'. Vif-'Heir th'e =-vertical di# rector 32 and the horizontal direc-tor SfI-have'ffad justed fthe beam iso ythat 'th'e maximum 'lect'i-in theFphctodetector '415 is achievedlthen the-"Signal reversal Sco-unter I I connectsu ground'to tlie'zcn-` ductcr E22 which istransnlttecrr througlith'ej armature 5 and front contact of the'TCrelayBS' to operate v-the clamp vrnagnetsf'and I2'3. These clamp magnets vtlfiereupon secure` 'themlrrors "59 and Sil-inf the `positionsY to which*"theyhavebeen moved 'iso upon -thel'o'realt incommnicatin between'` the precision-battery connected tofthe armatures 'I' andlof 'the CC `relay f' 84" 'and fthe beamffdirectors '51" andi 6 2i the 'mirrors' 59"and"' 6 DI wiufb'e mammuccari-position sothatithe:desees: tionsofthefbeamwillremain'ied.

In'the lowerpart of Fi'gfifthe action described' plotted against time. The graph of voltage on conductor I I I is shown as beginning from the time that the voltage on the conductor Hi becomes effective. At this instant the dierentiator I|3 produces a positive pulse and thereafter the generator II5 is in operation. When the Voltage then begins to diminish a negative pulse is-generated and the generator H5 becomes effective. The response of the generator IIE falls very quickly and boosts the voltage of the conductor III upwardly again whereupon another positive pulse is produced by the diierentiator I I3. This action is followed as pictured until the maximum voltage is achieved which means the maximum light is being received by the photodetector 46. 'Ihe lowermost graph shows that upon the last positive pulse produced by the differentiator I|3 the conductor |22 is grounded which results somewhat later in the operation of the clamping magnets 63 and |23. The signal reversal counter |I4 also at this time grounds the conductor |24 to operate the main anode relay 'I3 and thus disconnect the main anode potential from the conductor l5. This will also release the RS relay 'I4 so that the ground applied to the register for enabling it and for enabling the number group is removed thus returning these devices to normal.

In connection with these graphs it need be noted at the present that the rise of voltage in ,the conductor |IIl is accompanied by the rise of current in the LCS relay winding 79, so that this relay responds and by operating its armature 3 opens the circuit for the CC relay 84. However, and the point to be mentioned here is that, the action of the beam positioning circuit shown in Fig. 4 takes place in a matter of a few hundred microseconds, Whereas it takes the relay 'I9 and thereafter the relay 84 a number of milliseconds to operate so that the impulse to operate the relay 'I9 and to release therelay 84 is coincident with but far longer in poini-l of time than the operation of the beam positioning circuit.

After the beam has been properly positioned and has come to full brilliance then the reflection of that beam from the retrodirective mirror 42 will extend back to the trunk appearance and will affect the photodetector 65. This increases the current flow therein which may be traced from battery through a coil of the hybrid coil 66, the photodetector 65, the winding of the TLS relay 'I8 to ground. When no light strikes the photodetector 65 the current flow through the relay 'IU is insufficient to cause the operation of this relay butr as soon as the light beam is established the photodetector 65 is energized and the increase of current in the relay 'I8 is suicient to cause its energization.

Through its armature 3 and front contact the TLS relay 'I8 establishes a direct connection to the lamp 55 to hold this at full brilliance independent of the thermistor |01 during the use of the trunk.

Upon the operation of the TLS relay 'I0 the TC relay 99 is deenergized and therefore releases. As the beam comes to full brilliance and the photodetector 46 passes more vcurrent the relay 'I9 operates and releases the CC relay 84 asvdescribed. Relay 19 connects a source of positive battery to the main cathode of the line tube 'I8 so as to render this tube incapable of firing if a connection should be directed toit While the line 5,2 is in use. Ground jis connected through the front 'contact .and armatureft ofthe LCS relay I9 to maintain the shutter 43 opened during the use of the established connection.

When the subscriber station 52 rrelinquishes the connection the line relay 58 will become deenergized whereupon the LCS relay will release and in releasing will release the shutter magnet 44 so that light from the distant beam willbe shut 01T and the reflected beam will be interrupted and no signal is returned to the photodetector 65. The current through photodetector 65 reduces to the point where the TLS relay I8 releases and lamp 55 is extinguished. Thus the connection is released.

Means for establishing a connection to the line are very roughly indicated. A broken line rec-'- tangle |25 in Fig. 5 shows a trunk register |26 which may be set by signals sent over an incoming trunk to operate a number group |21. This number group I2I shows three conductors leadeing therefrom to the line tube 'I8 so that the tube may be fired in a similar manner to that described in connection with the trunk tube 69, that is, the tens wire may be grounded, the units to the short gap may be connected to a source of positive potential to break down this short gap. If this happens the hundreds wire connected to a longer gap and connected also to a source of positive potential will then transfer the electron stream within the tube. It may be noted that this tube will select any one of the lines designated by the three last digits, the selection of the thousands digit may be made between the trunk register and the number group, that is, the trunk register may activate one of ten number groups for this purpose. If the gap between the anode connected to the hundreds wire and the cathode connected to the tens wire breaks down and the line is idle, then'an electron stream vwill be established between the main anode 'II andthe main cathode 83 and during the operation of this tube locking will be provided by the resistance 'I6 and the associated inductance. The current then ilowing through this circuit operates the CC relay 84 and through the agency of a ringing control circuit I 28 the RC relay v5I is operated. This locks into operation through the back contact of the ringing trip relay 52 so that the common control may be dismissed as soon as the beam from the incoming trunk appearance to the line has been established. As soon as the CC relay 84 is operated then the precision battery terminals characterizing this particular line will be connected to the conductors |88 and I09'to position the beam in the same manner as that hereinbefore described. It should be noted that in all cases the operation of the connecting relays such as the relay 84 and the relay 99 occupy a very small interval since the operation of the register of the number group and the beam positioning circuit is very rapid.

The ringing control relay is now in operation and this may operate over a comparatively great length of time. When the subscriber at station 52 answers, then the ringing trip relay 52 responds and this releases the RC relay 5|. Immediately thereupon the line relay 58 is operated to hold the connection in the manner hereinbefore described.

Should the called subscriber at substation 52 fail to respond, then the release of the connection over the incoming trunk by the release of a supervisory relay in that circuit Will out off the beam and thus release the LCS relay'i. The

LCS relaywill open the holding circuit for Vthe RC relay 5 1 and thus-release the connecticm.`

@Sea-eee diiere'nce in this arrangement isthe use of an` electronic number group and an electronic busyand idle test means. These are shown Fig. -7'. The lcircuit of Fig. 6 is ralmost the same as the circuit of Fig. 3 anddiers-fonl-y in the arrangiements for startingY Ithe trunk tube. These vdifferences will be explained but theremainderyof the'circuit will be assumed to operate -in-exactly the-same manner .as tha'toiV Fig. 3.

In Fig. "1 when the subscriber at substation 52 s--making a call andthe tube i8Y 'has -lred then"` the: main anodecurrent through ther` winding oi: relay [u/i111. operate this relay and by placing ground on conductor |3`| will enable theregister |32. When the information stored on the preset dial at ythe substation 52 is `transmittedtoil the register thenA this register will pick out one ofV a number of cathode-ray tubes suchV for instance, asl the H9 tube |33 through the electrical selection Aof the individual wire |34. The cathode-ray produced this tube is now directed to a particular one .oi one hundred dynodes, let us say that one connected to the individual wire leading to the corre-V spondingly numbered trunk in Fig. 6.

'The normal-connections to the trunk tube 1:35 are as follows. The start cathode' of this tube is-connected` through armature 6 and back contact-ofl the TLS relay |31 toa source of negative potential (-"IOV volts). 'The start anode `o`f-this tube is connected through the armature 5 and back contact of' the TLS relay |31 to ground potential .through a` resistor |38. '-Ih'is start anode isalso connected tothef-wire |35 frorri` the cathodeeray tube. Letus assume that thepotential ofl a battery connected-to the-secondary collector grids o -the cathode-ray tubes by conduc-Y conductor |35and-thetrunkiwithwhichtheitrunk` tube. |36is associated is idle the eie'c'tive connection-made betweenthe dynode and thelsecondary collector gridwill cause a current to flow between the -l-IO'U-volt-battery and the ground potential at the back Contact of armature 5 of the TLS relay |21. Due to -the resistor |38 the change 1x1-.potential at the start anodev of the tube-1361's, by Way of example, from groundto-say +30 volts. The corresponding change ofpotentialA on conductor |39l from +100 volts to +30' volts, therefore, constitutes what may beterrned a strong pulse on conductor |-4|. Conductor I4! is oo nnected-in parallel tothe-two tubes |42 and' |-43-iri suona-manner that the tube |42--will immediately respond -to a large pulse such as that now'def scribed. tube therefore lires and tln-oiifg-h the1lockout connection betweenthe mainlanoples o ftlietubes |42 and |43 prevents the tube |343 from responding. Due to theconnectiofri` ofthe condenser I44and'theresistance |45 the'tube |143 issomewhat slow to respondsothat beforeit; can respond to1this large pulse on conductor .|.4llit is lockedout-through the operation of the tube |42'. Thus, if the trunk selected is idle the tube |42 will be red and the tube |43 will remain locked out. Due to the ring of tube |42 the conductor |46 corresponding to conductor |2 in Fig. 5 will gridY be affected to enable beam' positioning cie,-

cuit.

Let usl new' assume that the trunk isy busy .and that, therefore, the TLS` relay |31-v is operated.

In. this ease. the start cathode ofi the trrnkz tute i |36` is grounded (Zero potential) byarrnature .i6 and the start anodeis` *held at a; positive pote tialv (-I-:50 vol-ts', for" example). 'Iher"eier-el,` when e register taz has been setdnd the catncdesray" diirected to the dyno'de connected te conductor |35 the result will be a small pulse on conductor 114|l for the connection ofi 50 volts through the resisl tot |38 to: the conductor-f 13e will producefyomy a smania-range iin-.potential ascompa'red with that produced in the-previous. case; l'rite' tube mi wm not respond to such a sinall--pulsebutthetube 43 will'doth-isiliy time?. Therefore, the-tube fl'l) Wifi-lnreand in tnesame manner wiil iock out the t te |42. The tube |43 willnow-afieet aconductorf |41: which may be used in the salme `manner.asli rel-v inbefore described to established a beaniiromi a busy! trunk circuit-to supply busy -toneltothefcallling subscriber.

A callv in the other direction, that is;v from anY incomingl trunk` tovthe called subscriber at sub#- station 52-will be' handledA the same manner-asi described in rig.Y 5. that is, afatilty ttt-92 rnc-miti'- ing atrunkregister |550 andan-electronic-nuriiber` group represented by the cathode-ray tube F5-If' will be employed to' receive and --reg-ister the-1h1- cOlIliIlg identification o f the called part-y.

Through the electronic number group arrange#- ment then the conductor |152leadinein this case to the start anode of the line tube -1-8 will'be at; footed and the @all to this Substao'rl B Siehllld- In all other @Sheets the @relation O fl thai/,f v`i' 011s delicias are the Same as described .ijn Geer-'- tion with the arrangement ,of heures shown in Fig. l0.

What is claimed is;

1- A beamswitchlrle telecQmmuIliCatln ,SYS- tem comprising a plurality of subscribers" lines" and" a line at a distant point, a ,beam relief 0i' individual to each said subscribers line'J .S91 l redentor consisting; ojftjhe surfaces cqntiguoustjf theintersectin-of three mutually perpendicular reiiecting. surfaces, a light sensitiyedevice formed. 0n one of ,Saidrelectine Surfaces and-respons@ to the modulations of. a lightbeam directedlnto .Saidreeevor. means fizrvibraiinsanpilie one of the said reflecting. A sur-facesfor modul light beam ,reflected by' Said reflector, Sa., .Y Sensi-.tive devi-0el and-Said vibra-tine me beine Connected t0 the said-.Subscribers,line-.to-Which Said reefor :individua-1.. for' translating 1n- Comine 'beam signalsto ,electrical sien-@1S- and outepihe electrical signalsA to zbeam sgna1s..-andmeansv individual -to-,said line 1atta distant .point for Aselectively directing va beamtoward the re.'-Y

flectcr of a desired .one :of .said subscribers! lines,

said-distant -point meansl also lncludinga light sensitive device and a 'light controlling: device* connected to-said"'line thereat.V

-2.- A'beam kswitching telecommunication system Acomprising-a plurality of?subscribersy lines;

a beanirefiector individual to each-said' line, vsaid'- reflector consisting oflv the sLuifaceslcohti-guoustoa point defined `by --the intersection of tl-"ivres mutuallyperpendicular reflecting suriajes; a

light sensitive device4 mounted in cooperative" relationship with each said reflector and responsive to a fraction of a beam directed into said reflector, a light controlling device interposed in the path of a beam reflected by said reector, said light sensitive device and said light controlling device being connected to the said subscribers line to which said reflector is individual for translating incoming beam signals to electrical signals and outgoing electrical signals to beam signals, a link circuit at a distant point including a pair of devices each including means for di recting a .beam toward one of said reflectors, a light sensitive device and a light controlling device connected tc a line thereat whereby a connection may be extended between two of said lines by a pair of beams each directed to one of said lines by said link circuit, a line circuit for each of said'lines, means included therein for identifying itself and subscriber operated means for identifying another line to which a connection is to be extended, a common control means responsive to said identifying means, and means under control of said common control circuit for controlling the said beam directing means of said link circuit.

3, A beam switching telecommunication systern comprising a switching room, a plurality of subscribers lines, apparatus individual to each of said lines mounted at regularly spaced intervals on one wall of a switching room, each said line apparatus including a beam reflector consisting of the surfaces contiguous to a point defined by the intersection of three mutually perpendicular reflecting surfaces, Va photodetector mounted to intercept a fractional vportion of a light beam directed into said reflector, a light modulating device mounted in the path of a beam reflected from said reflector and means for blocking a beam into and out of said reflector, a plurality of other line circuit apparatuses mounted on a distant and parallel wall of said switching room, a light modulating device in the path of said beam, a photodetector mounted to be in the path of and responsive to a beam reected from a distant beam reflector and a pair of beam directing devices, a source of light for establishing a beam and a thermistor in series therewith for delaying the establishment of said beam, 4each said line apparatus being characterized by a predetermined signal which communicated to said beam directors will cause a beam established to be directed to said line apparatus, said thermistor consisting of a circuit element responsive to current therethrough to limit the rate of increase of the said current to delay the establishment of a said beam until said beam has been directed to said line apparatus whereby the-sweeping of an established beam over other line appearances will be avoided,

4. A beam switching telecommunication system comprising a switching chamber, a plurality of subscribers lines each terminating in a line apparatus mounted on the surface of one wall of a switching chamber, each said line apparatus including a beam reflector consisting of the surfaces contiguous to a point defined by the intersection of three mutually perpendicular reflecting surfaces, a receiver consisting of a photo-n detector mounted to intercept a fractional portion of a beam directed into said reflector, a transmitter consisting of a light modulator arranged in the path of a beam reflected from said reector. a beam intercepting device in the path of a beam entering and leaving said reflector responsive to the subscribers use of said line, and

a plurality ofother line apparatuses mounted on an opposite and parallel wall of said switching sponsive to a beam reflected from a distant reflector, certain of said other line apparatuses being connected to special signal sources, means for selecting a desired one of said other line apparatuses, and means responsive to the busy condition thereof for automatically activating one of said special signal line apparatuses.

5. A beam switching telecommunication system comprising a switching chamber consisting of an enclosed space having beam establishing and beam ypointing devices arrayed on one surface thereof and corner reflectors arrayed on an opposed surface thereof, each said beam establishing device consisting of a beam source and having mounted in cooperative relationship therewith a pair of beam deflecting mirrors each mounted on electro-responsive moving means for directing said beam in selected directions, a beam modulating means interposed in the line of said established beam and a photodetector mounted to intercept a reflection of said beam, a communication channel individual to each said beam establishing -device interconnected with said modulating means and said photodetector for transmitting signals from and receiving signals into said communication channel, each said corner reflector having individual thereto a beam modulating means interposed in the line of a beam directed into said reflector and reflected therefrom, a photodetector mounted to receive a portion of a beam directed into said reflector, a communication channel individual to each said corner reflector interconnected with said modulating means and said photodetector for transmitting signals over a beam reflected Iby said corner reflector and for receiving signals over a beam directed into said corner reflector, each said communication channel being electrically and separately identified and means for communicating the said electrical identification of a said communication channel to a distant beam establishing device for controlling the said beam deilecting mirrors thereat to point a beam therefrom to said identied associated corner reflector.

EDMOND BRUCE. LEO GROSS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,384,014 Fessenden July 5, 1921 1,771,143 Sprague July 22, 1930 2,224,677 Hanscom Dec. 10, 1940 2,235,803 Carpenter Mar. 18, 1941 2,241,031 Holden et a1. May 6, 1941 2,287,881 Holden June 30, 1942.. 2,293,899 Hanson Aug. 25, 1942 2,345,445 Atwood Mar. 28, 1944 2,387,018 Hartley Oct. 16, 1945 2,432,984 Budenbom Dec. 23, 1947 2,443,643 Schelleng June 22, 1948 2,477,821 Potts Aug. 2, 1949 

